How to use both cameras on iOS?

Does anybody know how to use both cameras as input in iOS? I don't need to display both cameras' view, but I try to do so for testing. I create two CvVideoCameraDelegate connected to two imageviews. Running the app, only one view shows the live camera view, the other one shows a static picture.

Any suggestion on that? I need my app to show only the back camera view and use front camera view as input at the same time.